Originally Posted by
2manybikes
You have it right. If you have a compact crank 10 speed with 34 and 50 rings. You can put on an 11-34 cog set. Then your low gear is 1 to 1 or 34 teeth to 34 t. Same as 36 to 36. A ten speed derailleur will not work with a 10 speed road bike. Get a nine speed rear mtb derailleur. This is exactly what I have done on a climbing bike. It works great and I still have good close ratios in the middle of the cassette and a high gear of 50-11. That puts me at about 42 mph at 120 rpm. It makes me very happy. It's been in use for about 4,000 miles. That's a couple or years, I have 15 bikes, that also get mileage on them too.
The bike was all 105 Shimano. Now it has an LX rear derailleur. I think an XT cassette. You have plenty of high gears for training and for the hills no down side unless you are racing.
Then go train your brains out !! You're don't need any more equipment options.
I've got a Shimano 10-speed cassette for my steep climb setup --
HG81 SLX 10 Speed Cassette 11-36T
LX M581 Rear Derailleur Long Cage SGS, Not Rapid Rise (Might not be available anymore)
I bought these based on solid advise in a similar thread. These work perfectly with the Ultegra 6700 triple on the bike, and shift much more precisely/reliably than the cheap 9 speed MTB derailleur and SRAM cassette I used in the first iteration. Total cost was around $95. I already had a long enough chain, so figure that in.